About 3/4" max. The manual says 1"
I am running an 70A elastomer, it did have a 30A on there when I got it. This must have been very very soft. I am 12 Stone and 70A feels about right.
I re-made the damper assembly, and even if I do say so my self, it is a better set up than the original - especialy in material choice. The new elastomer is courtesy of SLIM from this website, he went to alot of effort to make the top out bumper as well as the main bumper.
It is a 1993 Merlin as previously stated, if you look in the Archeive on this site, John has uploaded scanned copies of the catalogue and the bike is shown. Its called the Merlin Supension.
As you can see my build is a sympathetic build, not a full on M900 1993 rebuild. But everything on it (to me anyway) seems right.
Boring side note: Page 3 of the scanned manual "What makes merlin different?" - the back ground to the page is the drawing of the internals of the softail damper.